1. Field
Exemplary embodiments of the present invention relate to a liquid crystal display.
2. Discussion of the Background
A liquid crystal display is one of the most widely used types of flat panel displays. A liquid crystal display is a display device that controls the amount of light passing through a liquid crystal layer by applying a voltage to electrodes to rearrange liquid crystal molecules of the liquid crystal layer.
A liquid crystal display may be formed to be thin, but may have a limited viewing angle. In order to overcome this drawback, various types of liquid crystal arranging and driving methods have been developed. As a method for implementing a wide viewing angle, much attention is being paid to a liquid crystal display in which two field generating electrodes are formed in one substrate.
A display device typically includes a thin film transistor for switching each pixel. The thin film transistor is a switching element having three terminals, which include a gate electrode configured to receive a switching signal, a source electrode configured to receive a data voltage, and a drain electrode configured to output a data voltage. Further, the thin film transistor includes an active layer as a channel layer, with the active layer overlapping the gate electrode, the source electrode, and the drain electrode. The active layer is usually made of amorphous silicon as a semiconductor material.
However, with the increase in display size, the development of thin film transistors which can be driven at ultra-high speed is needed. Particularly, amorphous silicon, which is usually used as the active layer, has a low electron mobility and requires expensive deposition equipment based on a vacuum process, for applying a chemical vapor deposition (CVD) method, a sputtering method, or the like.
Therefore, research is being conducted on the development of an oxide semiconductor that has a high electron mobility and can be subjected to a solution process, to perform a coating process or an ultra-low-cost printing process. Further, the necessity for a method which forms a wire using a metal with a low resistance, to increase current transfer speed, is gradually increasing.
However, when a data conductor such as a data wire or an electrode of a thin film transistor is formed of a metal with a low resistance, the data conductor may be oxidized by an insulating layer formed over the data conductor. In order to prevent the oxidation, a method of forming a data conductor as double layers or triple layers having different physical properties has been proposed. However, even when the data conductor is formed as double layers or triple layers, the side surface of a metal with a low resistance may be exposed, and even the top surface of a layer made of a metal with a low resistance may be exposed because the double layers or triple layers are etched at different speeds. Therefore, it is difficult to prevent the oxidization of the low resistance data conductor.
Further, as the channel length of a thin film transistor decreases, the characteristics of the thin film transistor are improved. During a process of patterning a semiconductor, an input electrode, and an output electrode, using one exposure mask, it is difficult to accurately control a height difference between photosensitive film patterns. Therefore, there is a limitation in reducing a distance between the input electrode and the output electrode.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and, therefore, it may contain information that does not constitute prior art.